Kinases are enzymes that catalyze the addition of phosphate to a molecule. The addition of phosphate by a kinase is called phosphorylation. When the kinase substrate is a protein molecule, the amino acids commonly phosphorylated are serine, threonine and tyrosine. Phosphatases are enzymes that remove phosphate from a molecule. The removal of phosphate is called dephosphorylation. Kinases and phosphatases often represent competing forces within a cell to transmit, attenuate, or otherwise modulate cellular signals and cellular control mechanisms. Kinases and phosphatases have both overlapping and unique natural substrates. Cellular signals and control mechanisms, as regulated by kinases, phosphatases, and their natural substrates are a target of research tool design and drug design.
Rapamycin is a triene macrolide antibiotic, produced by Streptomyces hygroscopicus, and which demonstrates anti-fungal, anti-inflammatory, anti-tumor and immunosuppressive properties. Rapamycin also indirectly inhibits the activity of the protein, mTOR, (mammalian target of rapamycin) which, under abnormal conditions, can promote tumor growth. There are two rapamycin analogs, RAD001 and CCI-779, that have shown anticancer activity in clinical trials. It is also desirable to develop direct inhibitors of mTOR as potential therapeutics.
Mammalian target of rapamycin (mTOR), RAFT1, and FRAP are the same enzyme, herein referred to as mTOR. mTOR can phosphorylate serine and threonine residues in protein or peptide substrates. Some cellular substrates of mTOR have been identified and are referenced in Brunn et al. 1997 J Biol Chem 272:32547-50; Burnett et al. 1998 Proc Nati Acad Sci USA 95:1432-7; Carlson et al. 2004 Biochem Biophys Res Commun 316:533-9; Carraway et al. 2004 Breast Cancer Res, 6:219-224; Gringas et al. 1999 Genes & Dev 13:1422-37; Isotani et al. 1999 J Biol Chem 274:34493-8; Minami et al. 2001 Genes to Cells 6:1003-15; Mothe-Satney et al. 2000 J Biol Chem 275:33836-43; Peterson et al. 2000 J Biol Chem 275:7416-23; Yokogami et al. 2000 Current Biology 10:47-50. While individual substrates or ligands have been identified and studied, mixed ligands linked together as polyligands that modulate mTOR activity have not been demonstrated before this invention. An aspect of the invention is to provide novel, modular, inhibitors of mTOR activity by modifying one or more natural substrates by truncation and/or by amino acid substitution. A further aspect of the invention is the subcellular localization of an mTOR inhibitor, ligand, or polyligand by linking to a subcellular localization signal.
Design and synthesis of polypeptide ligands that modulate calcium/calmodulin-dependent protein kinase and that localize to the cardiac sarco(endo)plasmic reticulum was performed by Ji et al. (J Biol Chem (2003) 278:25063-71). Ji et al. accomplished this by generating expression constructs that localized calcium/calmodulin-dependent protein kinase inhibitory polypeptide ligands to the sarcoplasmic reticulum by fusing a sarcoplasmic reticulum localization signal derived from phospholamban to a polypeptide ligand. See also U.S. Pat. No. 7,071,295.